Connection of Seismic Noise Properties in Japan and California with Irregularity of Earth’s Rotation

Abstract

The problem of the relationship of the properties of seismic noise with the irregular rotation of the Earth is considered. We study the median daily values of the multifractal singularity spectrum support width, the generalized Hurst exponent, and the seismic noise wavelet-based entropy on the networks of broadband seismic stations in Japan and California for the time interval 1997–2019. The first principal components of the noise properties in a half year moving time window are calculated. The coherence spectra are estimated both between the principal noise components in two regions and each principal component with a time series of the length of day (LOD). It has been shown that an increase in the power of high-frequency pulsations of LOD (for periods less than 6 days) is accompanied by a decrease in the coherence between the properties of seismic noise in Japan and California. The degree of synchronization of the response of changes in the properties of seismic noise in Japan and California to the irregularity of Earth’s rotation in a “long” moving time window of 5 years is estimated. For this purpose, the correlation coefficient and the “secondary” coherence spectrum between synchronous variations of the “primary” coherence spectra between the LOD and each of the main noise components obtained in the “short” half-year window, as well as their mutual correlation function, were calculated.